Treatment of lead alloy anodes



NOV 12 1968 l.. P. SUDRABIN ETAL 3,410,771

TREATMENT OF LEAD ALLOY ANODES Filed May 3, 1965 F/a/ i wl lmli'gmzlm,

Leon i? Sudm/'n BY Lubomyr L/szczyns/ry @MS04-Miam United States Patent O TREATMENT F LEAD ALLQY ANGDES Leon I. Sudrahin, Berkeley Heights, and Lubomyr Liszczynsky, Bloomfield, NJ., assignors, by mesne assignments, to Wallace & Tiernan luc., East Orange, NJ., a corporation of Delaware Filed May 3, 1965, Ser. No. 452,567 Claims. (Cl. 204-147) This invention relates to lead alloy anodes as used in the cathodic protection of steel structures and the like immersed in sea water or other brines and more particularly to procedures for treating such anodes to recondition them in situ.

Steel structures-eg., ship hulls, steel piling, condenser water boxes, traveling screens and the like-which are submerged in sea water or other chloride brines are highly susceptible to damage by corrosion. A convenient and effective way of preventing such corrosion is by means of a so-called cathodic protection system utilizing impressed current, wherein the structure to be protected is made the cathode of the impressed current system, direct current being passed from an external source through an anode immersed in the brine, and thence through the brine to the structure to be protected.

Lead-alloy electrodes are widely used as anodes in cathodic protection systems of the type referred to above. When such anodes are placed in service and impressed current is passed through them, at current densities in a range from about 2 to about 30 amperes per square foot of anode surface, a lm or layer of lead peroxide (PbOz) rapidly forms .on the anode surface, The peroxide layer thus produced is suitably conductive to electricity and has a low resistance contact with the underlying electrode metal. After the peroxide layer has formed, electrons are transferred through this layer and its junction to the lead alloy anode and thence to the positive terminal of the direct current source employed. The electrochemical effect at the lead peroxide surface is the oxidation of chloride ions in the sea water or brine to chlorine gas, Once the initial rapid formation of the lead peroxide lm has occurred, i.e., ordinarily within about one week of initiation of operation with continuous impressed current, consumption of the lead alloy anode by the electrochemical process proceeds at a very slow rate (viz ordinarily at a rate of not more than about 0.1 lb./ampereyear) and thus the lead alloy electrode behaves as a relatively nonsacrificial anode. That is to say, the peroxide film, being both electrically conductive and protective to the lead alloy surface, enables use of the lead alloy anode for cathodic protection without rapid consumption of the anode; as will accordingly be appreciated, establishment of a satisfactory peroxide film is very important for cathodic protection operation using these anodes.

Lead or lead alloy anodes of various compositions have been used in cathodic protection systems of the type described, examples of such materials including 1% silver- 99% lead alloy, 2% silver-98% lead alloy, 1% silver- 6% antimony-93% lead alloy, and pure lead with platinum microelectrodes (i.e., having platinum wires positioned at various locations on the pure lead surface). Anodes of all the foregoing materials are found to form satisfactory lead peroxide layers in service, whereas pure lead alone (without platinum microelectrodes) does not exhibit good peroxide nlm-forming properties. As used herein, the term lead alloy electrodes will be understood to refer to electrodes made of lead alloys having suitable peroxide film-forming properties and to include anodes of pure lead having platinum appendages.

Such lead alloy anodes are suitable for use in the protection of metallic (eg.` steel) structures submerged in ICC sea water or in other chloride brines having a salinity equal to at least about 20% of the salinity of sea water (e.g., brines having a salinity in a range from about 5,000 ppm. up to saturation concentration of chloride). Salinity of the specified level is necessary for development of the desired peroxide coating on the lead alloy electrode surface, since to establish this coating the brine in which the electrode is immersed .must be sufficiently conductive to enable attainment of a current density of at least about 2 amp/ft.2 at the anode surface. Accordingly, it is to be understood that the term chloride brine as used herein refers to sea water and other brines of suticient salinity to provide the conductivity required for an anode current density of at least about 2 amp/ft2.

Lead alloy anodes as described above are ordinarily very satisfactory for cathodic protection operation under the specified conditions. However, in some instances of use of such anodes, a marked increase in electrical resistance in the cathodic protection system develops after a period of time. This increasing resistance, which is of course highly undesirable, is found to be associated with cathodic protection operations wherein the impressed current is periodically or intermittently shut olf, and is understood to result from formation of a layer of lead chloride (PbCl2) beneath the layer of lead peroxide, i.e., between the peroxide layer and the lead alloy substrate. It is presently believed that during periods of current shutoff, free chloride ions present in the brine migrate through the peroxide layer and react directly with the underlying lead to form the lead chloride layer; this layer of chloride, which has comparatively high electrical resistance, disbonds the lead peroxide from the anode metal and thereby occasions the aforementioned increase in resistance of the anode.

The development of the electrically resistive lead chloride rlayer appears to be a cumulative effect of repeated shutdowns of current; thus in one instance of operation of an impressed current system using lead alloy anodes for cathodic protection of a steel piling supporting a pier, wherein the current was shut off during intervals when a vessel was tied up at the pier (periods of current shutoff averaging 2 days out of each 1l) days), noticeable increase in electrical resistance of the cathodic protection system began to develop after about live to six months of operation and then accelerated rapidly over the next two to three months. Similar formation of a lead chloride layer with concomitant increase in resistance may also occur during a single protracted interruption of current after formation of the lead peroxide layer, or under other conditions in which the anode current density drops below about 2 amp/ft?, eg., as when there is a fresh water runott1 around the anode that decreases the electrical conductivity of the brine in which the anode is immersed.

An object of the present invention is to provide procedures for reconditioning lead alloy anodes, on which an electrically resistive coating or layer has developed, to remove such layer and thereby to overcome the problem of increase in resistance associated therewith. Another object is to provide such procedures for reconditioning lead alloy anodes in situ in a cathodic protection system, in a facile, convenient and highly etfective manner. A further object is to provide such procedures for reconditioning lead alloy anodes in situ wherein the reconditioning treatment is effected by the cathodic protection system itself without any special or `additional equipment. Yet another object is to provide procedures for treating lead alloy electrodes, e.g., as to reconditifon such electrodes in situ in a cathodic protection system after development of a resistive lead chloride layer thereon, which so treat the electrodes that the treated or reconditioned electrodes are markedly less susceptible to chloride layer formation than an untreated anode, and can thus be used for very substantially longer periods of time before further reconditioning is needed. A still further object is to provide a lead alloy anode prepared by such treatment and hav ing significantly lowered susceptibility to chloride layer formation and increase in resistance, as compared with conventional lead alloy anodes. Still another object is to provide a cathodic protection system including a plurality of lead alloy anodes and adapted to effect reconditioning of such anodes.

To these and other ends, the method of the invention, as applied to treatment of a lead alloy electrode arranged as an anode in a cathodic protection system and having thereon a coating of lead peroxide and an underlying layer of lead chloride, broadly contemplates disconnecting the electrode as anode, reconnecting the electrode in situ as the cathode of an impressed current system, and passing direct current to such electrode, through the chloride brine in which it is immersed, from an anode also mmersed in the brine. The causticity (accumulation of hydroxyl ions) and vigorous evolution of hydrogen gas produced at the surface of the lead alloy electrode by the electromechanical cathode process incident to such passage of current serve both to chemically loosen and to mechanically remove the lead peroxide and lead chloride coatings thereon, leaving a bare metal electrode surface.

In the practice of the described method, it is preferred to utilize a current density (i.e., cathode current density) and duration of current fiow selected to subject the electrode under treatment to between about and about 50 ampere-hours per square `foot of lead alloy electrode surface. It is found that less than about 10 amp.-hr./ft.2 is ineffective to achieve significant improvement in the condition of the electrode. On the other hand, if treatment substantially in excess of about 50 amp.hr./ft.2 is ernployed, the excessive causticity produced at the electrode surface while it is connected as cathode would occasion destructive consumption of the lead of the electrode, owing to the amphoteric character of lead. It is presently particularly preferred to subject the electrode to at least about 25 amp.-hr./ft.2, this extent of treatment being found to effect complete removal of both the outer peroxide film and the underlying lead chloride film leaving a bare etched metal surface.

After completion of the described reconditioning treatment, the treated electrode is reconnected as an anode in the cathodic protection system and normal operation of such system is resumed with passage of direct current as before between the reconditioned lead alloy anode and the protected steel structure through the brine. As at the initial start-up of operation of the cathodic protection system, a layer of lead peroxide rapidly reforms on the ,lead alloy anode surface. It is found, however, as a further and particular feature of the invention, that the peroxide layer produced after the foregoing reconditioning treatment exhibits superior properties with respect to ability of the electrode to withstand periods of current shutoff without development of a lead chloride layer. That is to say, after the reconditioning operation, the resistance of the cathodic protection system remains low for a very substantially longer period than before reconditioning notwithstanding that operation of the system may be as before, i.e., with equivalent periods of intermittent current shutoff.

Further features and advantages of the invention will be apparent from the detailed description hereinbelow set forth, together with the accompanying drawings, where- FIG. 1 is an elevational view, partly schematic, of a cathodic protection system incorporating a lead alloy anode and installed for protection of a steel piling structure, the system being shown as arranged for performance of the present method of recondition the lead alloy anode;

FIG. 2 is a view taken along the line 2-2 of FIG. l; and

FIG. 3 is a schematic elevational view of a modified form of cathodic protection system arranged for performance of the present reconditioning method without use of supplemental anode structures.

Referring rst to FlGS. 1 and 2, there is shown, as an example of a steel structure to be protected against corrosion, a pair of spaced vertical steel H piles 10 arranged with their lower portions submerged in a body of sea water 11 so as to provide support for a pier or the like, and connected in a continuous metallic structure (not shown). A lead alloy electrode 12, shown as an elongated rod of a suitable lead alloy bent in the form of an inverted U, is suspended in the water 11 between the illustrated pair of piles 10 by a rope 14 of plastic such as Saran or other electrically nonconductive material. The rope is secured to the piles 10 by means of heavy duty l beam clamps 15, in such manner as to position the lead alloy electrode l2 at a locality half-way between the piles 10 and entirely submerged below the mean low water level 17 of the body of sea water 11, i.e., so that the electrode will not be damaged or displaced by floating ice or debris.

A lead wire 19 is connected to the electrode 12 and extends therefrom, for example in closely parallel relation with and fastened to the Saran rope 14, to one of the piles 10, where the lead wire passes through a conduit 20 to a junction box 21, e.g., located above the surface of the water. In the junction box 21, the lead wire 19 is spliced to an anode feeder cable 22; the latter cable eX- tends (e.g., in -a suitable conduit) to a rectifier 24 which constitutes the direct current power supply for the cathodic protection system. For ordinary operation of the cathodic protection system, the anode feeder cable 22 is connected to the positive terminal 26 of rectifier 24, as indicated by broken line 27, and the negative terminal 28 of the rectifier is connected (as indicated by broken line 30) to the steel structure comprising the piles 10, the electrode 12 thus being connected as anode, and the piling 10 as cathode, of `an impressed current system wherein the body of sea water 11 constitutes the electrolyte.

ln operation of the described cathodic protection system, after installation of the lead alloy electrode 12 with connections to the rectifier 24 as described above, direct current is passed continuously through the system from the rectifier, eg., at an anode current density of between about 2 and about 30 amp/ft2. The continuous passage of current through the described cathodic protection system, with the electrode 12 as anode and the steel piling 10 as cathode of the system, serves to protect the piling against corrosion under exposure to the sea water. During the rst week or so of such operation, a coating film or layer of lead peroxide (dark brown in appearance) develops on the surface of the anode 12, and thereafter consumption of the lead alloy of the anode proceeds at a very slow rate. However, in the event that the current fiow is intermittently shut off, or that conditions of operation are otherwise such that the current density at the anode surface drops below about 2 amp/ft2, a layer or film of lead chloride develops between the peroxide outer film and the underlying metal of the anode 12, with the result that over a period of time the electrical resistance of the cathodic protection system undergoes a substantial and undesirable increase.

In accordance with the present invention, to recondition the lead alloy electrode 12 after development of such lead chloride layer and consequent increase in resistance, the electrode 12 is made the cathode of an impressed current system, while being maintained in position, as shown, immersed in the body of sea water 11. For this purpose, an auxiliary or supplemental anode illustrated as a length of steel cable 32 may be submerged in the body of sea water 11 in appropriately spaced relation to the electrode 12. The electrode 12 is disconnected from the positive terminal of the rectifier 24 (i.e., disconnected as anode) and connected as a cathode; this may be accomplished by connecting the feeder cable 22 to the negative terminal of the rectifier 24 as indicated by line 34 in FIG. l, after breaking the connection 30 from the latter terminal to the steel structure 10. The positive terminal of rectifier 24 is connected to the supplemental anode 32, as indicated by line 35 in FIG. l.

With the electrode 12 and supplemental anode 32 thus arranged and connected in an impressed current system, reconditioning of the electrode is effected by passing direct electric current from the rectifier 24 through this latter system, i.e., from supplemental anode 32 through the body of sea water 11 to the electrode 12. In such operation, the current density provided at the surface of the electrode 12, i.e. the ycathode current density, may be of any convenient value, it being presently preferred to operate with a cathode current density between about 2 and about 20 amp/ft.2 since current densities in this range can be readily provided by rectifiers conventionally used in present-day cathodic protection systems; in other words, for operation at such current densities the rectifier ordinarily employed in the cathodic protection system may simply be reconnected (as shown) and used as the power supply for the reconditioning operation. However, cathode current densities outside the foregoing range may be used if desired.

More particularly, the current is passed as described, between the supplemental anode 32 and the lead alloy electrode 12 connected as cathode, at a current density and for a period of time mutually selected to subject the electrode 12 preferably to between about 10 amperehours per square foot of electrode surface (indeed very preferably at least about 25 amp.hr./ft.2 for assured complete removal of the electrode surface coatings) and about 50 amp.-hr./ft.2 By virtue of the generation of hydrogen gas and accumulation of hydroxyl ions at the surface of the electrode 12 during this treatment, the previously existing lead peroxide layer and the underlying layer of lead chloride are removed, leaving a bare surface of etched metal.

At the completion of the described treatment, the reconditioned electrode 12 is reconnected as anode of the cathodic protection system and the supplemental anode 32 is disconnected. The steel structure 10 is reconnected to negative terminal 28. Ordinarily operation of the cathodic protection system is then resumed as before and a new layer or film of lead peroxide rapidly develops on the surface of the electrode 12.

In this way, reconditioning of the lead alloy electrode 12 is provided in a facile, highly effective and convenient manner without displacing the electrode from its installed position in the cathodic protection system. Upon resumption of cathodic protection operation, it is found that the resistance of the system is again reduced to substantially that of the system before development of the lead chloride layer; and, as before, after the period of rapid formation of the new peroxide layer, consumption of the lead by the electrochemical process is very slow.

It is furthermore found that the reconditioned electrode 12 (i.e., the electrode after treatment in accordance with the method of the invention and after formation of a new film of lead peroxide on its surface) exhibits markedly decreased susceptibility to development of an electrically resistive lead chloride layer. That is to say, when the reconditioned lead alloy electrode is used as an anode in cathodic protection operation with intervals of current shutoff, the period of time elapsing before significant increase in electrical resistance begins to develop is very substantially longer than when a lead alloy anode which has not been treated by the present method is employed in such operation. This important and advantageous result is presently believed to be due to properties of enhanced adherence and nonpermeability of the lead peroxide coating which is formed after the reconditioning operation when the treated electrode is returned to service as an anode in the cathodic protection system.

While for simplicity of illustration a single lead alloy electrode 12 has been shown in FIGS. 1 and 2, connected between a single pair of piles 10, it will be appreciated that in practice a plurality of such electrodes may be employed in a single cathodic protection system, for protection of a larger number of steel piles (or for portection of other structure), the electrodes being connected in parallel to the positive terminal of the direct current power supply. In such case, the reconditioning treatment described above may be simultaneously applied to all these electrodes by connecting the line of parallel electrodes to the negative terminal of the power supply and providing a supplemental anode (connected to the positive terminal of the power supply), such as an elongated length of steel cable 32, disposed in siutably spaced relation to the array of electrodes to be treated.

An alternative and especially convenient arrangement, for the practice of the present method in cathodic protection systems employing a plurality of anodes, is illustrated schematically in FIG. 3. In this figure the steel structure to be protected is represented as a continuous metal structure of steel piles 40 the lower portions of which are submerged in a body of sea water 42. Suspended in the body of water 42 in spaced relation to the steel piles 40 is a first group 44 of lead alloy electrodes and a second group 46 of such electrodes. For cathodic protection operation, both groups of electrodes 44 and 46 are connected in parallel to the positive terminal 47 of a rectifier 48 and the steel structure 40 is connected to the negative terminal 49 of the rectifier so that current iiows through the sea water between the electrodes 44, 46 (connected as anodes) and the steel structure 40 (connected as cathode).

More particularly, in the system of FIG. 3 the two groups of electrodes 44 and 46 are connected in separate circuits, respectively represented by lead wires 50 and 51, with the electrodes of each group connected in parallel. Switch means are provided for individually connecting the two wires 50 and 51 in parallel to the positive terminal 47 of the rectifier through wire 53, such means being arranged so that either group of electrodes may be disconnected from terminal 47 while the other group remains connected thereto; and switch means are also provided for selectively connecting wire 55 from the negative rectifier terminal 49 to the steel piling 40 (through lead wire 56) or to either of the electrode groups 44 and 46 when such group is disconnected from positive terminal 47.

As one example of a suitable switching arrangement, the lead wires 50, 51 and 56 may respectively terminate in contact points 57, 58 and 59 within a switch box 60. In the box 60, switches 62 and 63 respectively cooperate with contact points 57 and 58 to individually connect lead wires 50 and 51 to positive terminal 47. In addition, the three contact points 57, 58 and 59 are all arranged to cooperate with a three-way switch 66 which is connected at point 68 to wire 55 from the negative terminal 49 and is selectively positionable in contact with any of points 57, 58 and 59 so that any one of the lead Wires 50, 51 and 56 may be connected through switch 66 to the negative terminal 49. For ordinary operation of the cathodic protection system, as shown in FIG 3, switches 62 and 63 are closed (connecting both electrode groups 44 and 46 in parallel to the positive terminal 47) and switch 66 is positioned in contact with point 59 to connect the piling 40 to the negative terimnal 49.

The system of FIG. 3 is arranged to effect reconditioning of the lead alloy electrodes 44, 46, when an electrically resistive lead chloride film has developed on the electrodes, without use of any auxiliary or supplemental anode. For such reconditioning, switch 62 is first opened, disconnecting the electrode group 44 from positive terminal 47, while siwtch 63 remains closed; switch 66 is then moved out of contact with point 59 (disconnecting the piling 40 from negative terminal 49) and into contact with point 57, to connect electrode group 44 to negative terminal 49, so that electrodes 44 are connected as cathodes, and electrodes 46 as anodes, of an impressed current system supplied by rectifier 48. Current is then passed through the body of sea water 42 between the electrodes thus connected, at a cathode current density and for a period of time sufficient to remove the peroxide and chloride coatings from the lead alloy electrodes of group 44, i.e., preferably to subject the electrodes of group 44 to between about l amp.-hr./ft.2 (very preferably at least about amp.hr./ft.2) and about 50 amp.hr./ft.2.

When the treatment of electrodes 44 is completed, the connections of the two electrode groups are reversed by adjustment of the switches in box 60, so that the electrodes of group 44 are connected as anodes (to positive terminal `47) and the electrodes of group 46 as cathodes (to negative terminal 49). Current is again passed through the system, under the same conditions as before, to recondition the electrodes 46 by effecting removal of the surface coatings therefrom. After both groups of electrodes have thus been reconditioned, they are returned to service as anodes in the cathodic protection system by returning the switches to the position shown in FIG. 3, with both switches 62 and 63 closed and switch 66 in contact with point 59 to reconnect the piling 40 to the negative terminal 49.

As will now be appreciated, in the embodiment of procedure just described the reconditioning method of the invention is performed in the same manner as in the case of the system of FIGS. l-2 above, except that instead of using an auxiliary anode 32, each of the two separately connected electrode groups 44 and 46 of the cathodic protection system itself is used as anode for reconditioning the electrodes of the other group. In other words, as exemplified by the arrangement of FIG. 3, in cathodic protection systems having at least two circuits of lead alloy electrodes immersed in a chloride brine and separately connected as anodes to a direct current power supply, the present reconditioning treatment may be effected by connecting one of the electrode circuits to the negative terminal of the power supply while maintaining another of the electrode circuits connected to the positive terminal, and passing current between these oppositely connected circuits of electrodes through the brine; the circuit or group of electrodes which is connected to the negative terminal, i.e., as cathode, is thereby reconditioned and may itself subsequently `be used as anode to treat the other circuit or circuits of electrodes. Reconditioning of the electrodes is thus effected in a manner obviating the necessity for provision of auxiliary anodes.

While the invention has been described above with particular reference to the reconditioning of lead alloy anodes used for cathodic protection of steel piles immersed in sea water, the method may also be used for the treatment of lead alloy anodes immersed in other chloride brines as described herein, and arranged for protection of any type of steel structure submerged in or exposed to such brines. Moreover, the method is not limited to any particular form or composition of lead alloy anodes, but may be used to treat any lead alloy electrodes as defined herein.

Indeed, while reference has been made above to the use of the present method to remove the adherent lead chloride film and overlying lead peroxide film from a lead alloy anode after an extended period of service of such anode, and while the invention in this aspect has special advantages as providing a highly effective and convenient treatment for reconditioning electrodes so coated, the invention in a broader sense also embraces the pretreatment of newly installed lead alloy anodes, i.e., being applicable to treat such electrodes even -before they are put in service in normal operation of a cathodic protection system and before development of any peroxide or chloride surface coatings thereon. That is to say, after a new lead alloy electrode is immersed in a chloride brine in position for use in a cathodic protection system, it may initially be connected as a cathide to the negative terminal of a direct current power supply and current may then be passed to this electrode through the Ibrine from an anode also immersed in the brine. The treatment may be effected in the same manner as described above for reconditioning a coated electrode after a period of service, and provides the advantages already noted with respect to significantly decreased susceptibility of the treated electrode to development of the increased resistance condition by formation of lead chloride in use as an anode of a cathodic protection system.

By way of further and more specific illustration of the method of the invention reference may be made to the following specific example of such method as applied to the treatment of lead alloy anodes in a cathodic protection system arranged for protection of steel piles of a pier immersed in sea water. In the cathodic protection system of this example, twenty-four lead alloy anodes (comprising rods of 1% silver-99% lead alloy each 11/2 inches in diameter and l0 feet long and having a total surface area of about 3.9 ft2) were suspended in the sea water between the piles in the manner shown in FIG. 1 and served to protect a total of approximately 100,000 ft.2 of submerged steel surface. Two rectifiers were employed in this system, each connected to supply direct electric current to twelve of the anodes. The total current supplied by each rectifier to the twelve anodes (which were connected in parallel) was about 400 amp. at about 8 to 9 volts.

In the operation of this cathodic protection system the total current through each set of twelve electrodes was initially about 390 amp. at 7 volts. The system was operated continuously, except that the current was shut off for an average of about 2 days out of every l() days (i.e., during periods when tanker vessels were tied up at the pier). After 5 to 6 months of operation a significant increase in the electrical resistance of the cathodic protection system began to appear. Thereafter this increase accelerated rapidly, and has become severe by about 8 to 9 months after the start of operation; as a result, by the latter time the total current through each set of twelve electrodes had dropped to about 160 amp. at l0 volts.

In accordance with the present method, an -foot length of one inch diameter scrap steel cable was submerged in spaced adjacent relation to one set of twelve lead alloy electrodes (which were maintained in position submerged in the sea water). The cable was corinected to the positive terminal of the rectifier supplying this set of electrodes; the latter electrodes were connected to the negative terminal of the rectifier. A total current of about to 120 amp. supplied by the rectifier at about 101/2 volts was then passed from the cable anode through the sea water to the twelve electrodes for a period of l2 hours. Since the current through each of the latter electrodes was about 10 amp., the current density (i.e., cathode current density) at the surfaces of the electrodes under treatment was about 21/2 amp/ft2; hence over the 12-hour treatment period each lead alloy electrode was subjected to about 30 amp-hr. per square foot of electrode surface. The same treatment was then applied to the other set of twelve electrodes.

After this treatment was completed, the surfaces of the treated electrodes exhibited a clean, bare metallic appearance (as determined by underwater visual inspection), indicating complete removal of surface coatings. When the electrodes were reconnected as anodes and returned to service in the cathodic protection system, it was found that the increased electrical resistance condition present before treatment had been overcome. Upon initial resumption of cathodic protection operation, the total current through each set of twelve electrodes was about 400 amp. at 8 volts. Operation was continued as before, i.e., with current interrupted on an average of 2 days out of every l0` One year later, the total current through each set of twelve electrodes was about 300 amp. at 8.5 volts; and even after 17 months of such operation, only a relatively slight increase in electrical resistance of the system was observed, as compared to the severe increase in resistance which had developed after only 8 to 9 months of operation before the electrodes were treated as described above. This very marked increase in length of time elapsing before development of enhanced resistance indicated that the susceptibility of the lead alloy electrodes to formation of an electrically resistive lead chloride lm had been significantly reduced as a result of the present reconditioning treatment.

It is to be understood that the invention is not limited to the procedures and embodiments hereinabove specifically set forth, but may be carried out in other ways without departure from its spirit.

We claim:

1. A method of treating a lead alloy electrode immersed in chloride brine and positioned to serve as an anode in a cathodic protection system for protection of metallic structure exposed to said brine, said method comprising connecting said electrode as cathode of an impressed current system while maintaining lsaid electrode in position immersed in said brine, and passing direct electric current through said brine between an anode immersed in said brine and said electrode, `to effect cleaning of the surface of said electrode.

2. A method of treating a lead alloy electrode immersed in chloride brine and having an electrically resistive surface coating and positioned to serve as anode in a cathodic protection system for protection of metallic structure exposed to said brine, said method comprising connecting said electrode as cathode of an impressed current system while maintaining said electrode in position immersed in said brine, and passing direct electric current through said brine between an anode immersed in said brine and said electrode, to effect removal of said surface coating from said electrode.

3. A method of treating a lead alloy electrode immersed in chloride brine and having an electrically resistive surface coating and positioned to serve as anode in a cathodic protection system for protection of metallic structure exposed to said brine, said method comprising connecting said electrode as cathode of an impressed current system while maintaining said electro-de in position immersed in said brine, and passing direct electric current through said brine between an anode immersed in said brine and said electrode, at a cathode current density and for a period of time selected to subject said electrode to at least about l ampere-hours per square foot of electrode surface for removal of said surface coating therefrom.

4. A method of treating a lead alloy electrode immersed in chloride brine and having an electrically resistive surface coating of lead chloride with an overlying outer coating of lead peroxide and positioned to serve as anode in a cathodic protection system for protection of metallic structure exposed to said brine, said method comprising connecting said electrode as cathode of an impressed current system while maintaining said electrode in position immersed in said brine, and passing direct electric current through said brine between an anode immersed in said brine and said electrode, at a cathode current density and for a period of time selected to subject said electrode to between about 10 and about 50 ampere-hours per square foot of electrode surface for removal of said surface coatings therefrom.

S. A method according to claim 4, wherein said cathode current density and period of time are selected to subject said electrode to at least about ampere-hours per square foot of electrode surface.

6. A method according to claim 4 wherein said cathode current density is between about 2 and about 20 amperes per square foot.

7. A method of treating a lead alloy electrode immersed in chloride brine and having an electrically resistive surface coating of lead chloride with an overlying outer coating of lead peroxide and positioned to serve as anode in a cathodic protection system for protection of metallic structure exposed to said brine, said method comprising connecting said electrode as cathode of an impressed current system while maintaining said electrode in position immersed in said brine, passing direct electric current through said brine between an anode immersed in said brine and said electrode at a cathode current density and for a period of time selected to subject said electrode to between about 25 and about 50 ampere-hours per square foot of electrode surface for removal of said surface coatings therefrom, reconnecting said lead alloy electrode as anode of said cathodic protection system, and passing direct electric current through said brine between said lead alloy electrode connected as anode and said metallic structure connected as cathode at an anode current density of between about 2 and about 30 amperes per square foot.

8. A method of `reconditioning lead alloy electrodes in a catho-dic protection system for protection of metallic structure exposed to a chloride brine, wherein said system includes at least two lead alloy electrodes connected in parallel to the positive terminal of a direct current power supply to serve as anodes of said cathodic protection system and wherein each of said lead alloy electrodes is immersed in said chloride brine and has as electrically resistive surface coating of lead chloride with an overlying outer coating of lead peroxide, said method cornprising, while maintaining said electrodes immersed in said brine, connecting at least one of said alloy electrodes to the negative terminal of said power supply while maintaining at least one other of said electrodes connected to said positive terminal, and passing di-rect electric current through said brine between said other electrode and said one electrode at a cathode current density and for a period of time selected to subject said one electrode to between about 10 and about l5 ampere-hours per square foot of electrode surface for removal of said surface coatings therefrom.

9. A method of reconditioning lead alloy electrodes in a cathodic protection system for protection of metallic structure exposed to a chloride brine, wherein said system includes at least two lead alloy electrodes connected in parallel to the positive terminal of a direct current power supply to serve as anodes of said cathodic protection system and wherein each of said lead alloy electrodes is immersed in said chloride brine and has an electrically resistive surface coating of lead chloride with an overlying outer coating of lead peroxide, said method comprising, while maintaining said electrodes immersed in said brine, connecting at least one of said electrodes to the negative terminal of said power supply while maintaining at least one other of said electrodes connected to said positive terminal, passing -direct electric current through said brine between said other electrode and said one electrode at a cathode current density and for a period of time selected to subject said one electrode to between about 25 and about 50 ampere-hours per square foot `of electrode surface for removal of said surface coatings therefrom, reconnecting said one electrode to the positive terminal of said power supply, connecting said other electrode to the negative terminal of said power supply, passing direct electric current through said brine between said one electrode and said other electrode at a cathode current density and for a period of time selected to subject said other electrode to between about 25 and about 50 ampere-hours per square foot of electrode surface for removal of said surface coatings therefrom, reconnecting said other electrode to said positive terminal in parallel with said one electrode :as anodes of said cathodic protection system, and passing direct electric current through said brine between said electrodes and said metallic structure connected as cathode of said cathodic protection system at an anode current density of between about 2 and about 3() amperes per square foot.

10. In a cathodic protection system for protection of metallic structure exposed to a chloride brine, the combination, with said metallic structure, of first and second lead alloy electrodes immersed in said brine and positioned to serve as anodes of said cathodic protection system; means providing a source of direct electric current and having a positive terminal and a negative terminal; a iirst electrical connection to said first electrode; a second electrical connection to said second electrode; a third electrical connection to said metallic structure; switch means operable to connect said iirst and second electrical connections in parallel to said positive terminal and to disconnect either of said rst and second electrical connections from said positive terminal while maintaining the other of said iirst and second electrical connection connected to said positive terminal; and means for selectively connecting any one of said rst, second and third electrical connections to said negative terminal.

References Cited UNITED STATES PATENTS 1,984,899 12/1934 Smith t 204-147 2,149,617 3/1939 Menaul 204-147 2,805,191 9/1957 Hersch 204-195 2,945,791 7/1960 Gibson 1204-98 2,952,726 9/1960 Ilge et al 204-140 3,108,939 10/1963 Sabins 204-290 3,284,333 11/1966 Parsi et al. 204-290 HOWARD S. WILLIAMS, Primary Examiner.

T. TUNG, Assistant Examiner. 

1. A METHOD OF TREATING A LEAD ALLOY ELECTRODE IMMERSED IN CHLORIDE BRINE AND POSITIONED TO SERVE AS AN ANODE IN A CATHODIC PROTECTION SYSTEM FOR PROTECTION OF METALLIC STRUCTURE EXPOSED TO SAID BRINE, SAID METHOD COMPRISING CONNECTING SAID ELECTRODE AS CATHODE OF AN IMPRESSED CURRENT SYSTEM WHILE MAINTAINING SAID ELECTRODE IN POSITION IMMERSED IN SAID BRINE, AND PASSING DIRECT ELECTRIC CURRENT THROUGH SAID BRINE BETWEEN AN ANODE IMMERSED IN SAID BRINE AND SAID ELECTRODE, TO EFFECT CLEANING OF THE SURFACE OF SAID ELECTRODE. 